The Quest for the Meaning of Existence. You question your existence. You quest to find meaning for your existence. You seek the answers to the questions, "Who am I? Why am I here? What is my purpose? Why do I exist?" You exist for that quest.

Gork, "Why am I here? What is it that I'm supposed to do with my life?"
Charlie, "Those are questions we all ask ourselves at one time or another."
Gork, "But, why do I even exist?"
Charlie, "Quexistence. You seek the answers to your existence. You are on a quest to find those answers. You exist for that quest."

You question your existence. This generally happens after a whiskey nightcrawler, a night of trash and crash, blacking out ,or being blacked. You may ask yourself questions like, "Who am I?", "Where the hell am I?", "How the fuck did I get here?"
You may find yourself actually trying to answer these questions if you smoke marijuana, or have eaten shrooms, peyote, or mescaline, and you will find yourself on a quest to find the answers and meaning for your existence.

John and Pauljust woke up after a night of trash and crash and were smoking on a blunt.
John: "Where the fuck am I?"
Paul: "You're here, man."
John: "How the hell did I get here?"
Paul: "I don't know, man. Who the fuck are you?"
John: "I don't know. Who am I?"
Paul: "You're the man, man."
These stoners are in a state of quexistence.